1. Field of the Invention
This invention pertains to the field of cockpit indicators or head-up display units that provide terrain information to the pilot or flight crew of an aircraft.
2. Description of the Related Art
Modern avionics systems employ Head-Up Display (“HUD”) and Head-Down Display (“HDD”) indicating systems for providing tactical flight information to the pilot. In a HUD system, a HUD unit is mounted in front of the pilot at windshield level and is directly in the pilot's field of vision. The HUD system is advantageous because the display is transparent allowing the pilot to keep his or her eyes “outside the cockpit” while the display unit provides tactical flight information to the pilot. In a HDD system, a tactical flight display is mounted in the cockpit instrument panel directly in front of the pilot and below windshield level. To view the presentation of information on a display unit of a HDD system, a pilot must look down into the cockpit, causing him or her to take his or her eyes from the outside scene of the aircraft.
Modern avionics systems may employ Synthetic Vision Systems (“SVS”) for displaying terrain information to both HDD and HUD systems. The SVS system is advantageous in an HDD and HUD indicating system because it presents terrain information of the scene outside the aircraft, thereby enhancing the situational awareness of the pilot. In an HDD system, a lighted solid image of terrain and objects (e.g., obstacles and runways) may be represented on an HDD unit as a realistic, intuitive, three-dimensional perspective using terrain color coding according to elevation that mimics coloring used in aviation-related charts and publications.
In a HUD system, an image of terrain and its features may be rendered as a wireframe that presents a monochrome, three-dimensional perspective on a HUD unit. Testing in a cockpit simulator has demonstrated that a wireframe image tends to be difficult to interpret. Terrain features are not easily distinguishable on the wireframe image as they are on the HDD lighted solid image. Also, multiple terrain resolutions and high resolution data tend to clutter a wireframe image, and objects may be difficult to display in rendering a wireframe terrain image. In addition, a pilot tends to lose perception of the surface as the altitude of the aircraft approaches the elevation of the terrain.